1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling the revolution speed of an automotive engine having an automatic transmission and, more particularly, to a method of and an apparatus for controlling the revolution speed of such an engine in accordance with the condition of the engine when the load level is changed.
2. Description of the Prior Art
A modern system for executing the engine speed control of the type described above is disclosed in, for example, Japanese Patent Examined Publication No. 49-40886. In this system, actual engine speed is compared with a standard idle speed and an electrical valve disposed in a pipe by-passing a throttle valve is suitably opened and closed in accordance with the result of the comparison, thereby maintaining a constant engine speed. Another method for controlling idle speed of an engine disclosed in Japanese Patent Unexamined Publication No. 57-124042 employs means for computing the upper and lower limit values of engine speed when neutral state or drive state is selected in an automatic transmission, and these upper and lower limits of the engine speed are used as a function of the cooling water temperature in the control of the idle speed of the engine.
These conventional arts, however, do not take into consideration about the influence of load level change from no-load idle range (referred to as N range) to driving range (referred to as D range or R range) in an automobile having an automatic transmission. Operation of automatic transmission often encounters a problem in that the engine revolution speed is lowered due to a drastic change in the load particularly when shifting from N to D or R range, often resulting in an engine stall in the worst case. In other words, the gain of the feedback loop interconnecting the engine and the automatic transmission could not respond to the change in the load level.